Tocopherols are antioxidants and constitute the different forms of vitamin E. There are four principal homologues of tocopherols, namely, alpha (a), beta, gamma, and delta tocopherols. Although all four homologues of vitamin E exhibit activity, xcex1-tocopherol possesses the highest biological activity.
As a class of compounds, the tocopherols have been extensively studied. Through the findings of these studies, certain biological activities have been attributed to the tocopherols. Most notably, tocopherols possess strong antioxidant properties. Tocopherols function exquisitely in their ability to remove free radicals. Thus, tocopherols find a wide range of uses in a large variety of consumer products including foodstuffs and cosmetics.
There are several methods reported in the literature for isolating tocopherols from natural sources such as vegetable oils. Tocopherols can be separated by a series of distillation steps (U.S. Pat. Nos. 5,512,691 and 5,487,817). Liquid chromatography has also been employed to fractionate tocopherols (U.S. Pat. Nos. 3,402,182 and 4,122,094). Researchers have also utilized super-critical carbon dioxide to concentrate tocopherols (JP 60149582). However, all these reported processes suffer from technical drawbacks such as the requirement of toxic chlorinated solvents, special apparatus, large volumes of eluents, and/or acidic elution steps. Also, the maximum purity of tocopherols obtainable in these processes is relatively low (about 80-90%). Therefore, there is a need for an effective separation process for large scale production of more highly purified tocopherol compositions. It is even more desirable to produce highly purified preparations of xcex1-tocopherol.
This invention provides a method of separating tocopherols by using a weakly basic polyvinyl pyridine resin. The resin has the capacity to selectively bind tocopherols, allowing other impurities typically found in a tocopherol production plant stream to separate from the tocopherols. After loading a tocopherol-containing mixture onto a separatory column packed with the resin, the loaded column is eluted with a solvent followed by an alcohol. The eluate is collected in fractions, and the tocopherol-containing fractions are combined and concentrated to yield a purified tocopherol composition. It has been found that the present invention produces highly purified tocopherol compositions, and is particularly useful for preparing highly purified tocopherol compositions, specifically enriched in xcex1-tocopherol.
It has been found that a purified tocopherol composition can be prepared from a tocopherol-containing mixture by eluting the mixture through a separatory column packed with a polyvinyl pyridine resin. This method provides for a more purified tocopherol product than is available through known distillation, liquid chromatography and super-critical carbon dioxide extraction processes. The method of the present invention utilizes relatively innocus chemicals and does not require complex or specialized equipment. Thus, the process of the present invention may also allow for more economical production of tocopherols.
The present invention is directed to a method for preparing an enriched xcex1-tocopherol composition comprising:
i. providing a tocopherol-containing mixture wherein xcex1-tocopherol is present,
ii. placing the tocopherol-containing mixture onto a separatory column containing a polyvinyl pyridine resin,
iii. eluting tocopherols by washing the column with an organic solvent followed by an alcohol,
iv. collecting the eluate in fractions,
v. combining the fractions containing tocopherols, and
vi. concentrating the combined fractions to prepare a purified tocopherol composition enriched in xcex1-tocopherol.
In a preferred embodiment, the tocopherol-containing mixture is diluted with an organic solvent prior to adding to the column. Preferably, the ratio by volume of the tocopherol-containing mixture to the organic solvent is between about 1:0.5 to about 1:4. Most preferably, the ratio is about 1:2.
Any suitable solvent can be used in accordance with the present invention. Most preferably, the solvent is heptane or hexane.
It is envisioned that any suitable alcohol can be used in accordance with the present invention. In a more preferred embodiment, the alcohol is isopropanol, ethanol or methanol.
The flowrate of the solvent and the alcohol through the column can be adjusted independently to achieve maximum separation of the tocopherol from any impurities. Preferably, the flowrate of the solvent and the alcohol is between about 5 ml/min to 10 ml/min. More preferably, the flowrate for each is between about 8 ml/min to 9 ml/min.
The method of the present invention typically yields highly purified tocopherol compositions. Preferably, the xcex1-tocopherol content is between about 90 to 100% xcex1-tocopherol. Most preferably, the purified tocopherol composition comprises between about 95 to 100% xcex1-tocopherol.
The following examples demonstrate the efficacy of the method of the present invention for preparing a highly purified tocopherol composition. The tocopherol compositions produced by this method are comprised of at least 90% total tocopherols. Typically the alpha form comprises at least 95% of the total tocopherols in the product.
Generally, tocopherols are derived from vegetable oils, and produced in tocopherol production plants. The product stream from such plants may contain numerous impurities. As the examples illustrate, the present method can purify a typical tocopherol-containing admixture (ATD) produced from a large-scale tocopherol production plant.
This invention utilizes a weakly basic ion exchange resin. Preferably, the weakly basic resin contains pyridine functionality. More preferably, the resin is a polymer containing 2-vinylpyridine or 4-vinylpyridine functionality with suitable cross-linking agents, such as, divinylbenzene. The degree of cross-linking is 2-52%. Illustrative examples of this weakly basic resin are Reillex HP poly-4-vinylpyridine and poly-2-vinylpyridine resins (Reilly Industries, Indianapolis, Ind., USA).